Due to disease, trauma, or congenital malformation, the ossicles of the middle ear are sometimes damaged. The delicate joint between the incus and the stapes is termed the incudo-stapedial joint (ISJ). The ISJ is a cartilaginous joint having a tendency to ossify in older humans. When the joint is interrupted due to erosion of the joint or the incus itself, vibrations can no longer be transmitted from the incus to the stapes. The result is a conductive hearing loss related to the disrupted ossicular chain.
Medical implants have been developed to reconstruct the ossicular chain when a portion of the incus is missing. However, the entire incus has to be removed and replaced with a prosthesis. This approach destroys the natural joint between the incus and stapes and the lever function of the incus in relationship to the malleus and stapes.
One particular implant to address conditions when only the ISJ is eroded or ossified is shown in U.S. Pat. No. 5,306,299. This prosthesis is made from a hydroxylapatite. Particularly, the prosthesis comprises a block of hydroxylapatite having a cylindrical cavity intersecting with a U-shaped channel. The prosthesis cannot be adjusted to conform to various sized incus and stapes. As such, the prosthesis must be provided in different sizes for different size ossicular chains. Because of its mass and lack of features to stabilize its connection to the incus and stapes, it is possible for the prosthesis to migrate and extrude through the ear drum over a period of time. Concerns over the weight of the ceramic material and the overall mass of the prosthesis have been raised. Also, the hydroxylapatite material is inherently fragile, prone to breakage and cannot be easily modified to custom fit the incus or stapes head.
An alternative ISJ prosthesis is disclosed in U.S. Pat. No. 5,514,177. This prosthesis is formed of composite construction using pieces of different materials secured together such as by welding.
Certain ossicular prosthetics require that they be manually crimped to the bone. Fixating or crimping an ossicular prosthesis to bone can be difficult due to problems with prosthesis stability, surgical exposure, appropriate clamping, etc. It is desirable to have a prosthesis that is “self-crimping”. Ideally, the self crimping prosthesis should be low profile and provide secure, stable fixation. It should also be easy to apply without damaging the ossicles and apply a small amount of pressure to the ossicles so as to minimize the potential for pressure necrosis.
U.S. Pat. Nos. 6,197,060 and 6,554,861 describe various ossicular prostheses that include a shape memory wire or ribbon reversely turned on itself to form an open-ended bight. The bight is opened with a tool and then automatically closed and crimped about an ossicle upon the application of a signal such as heat. However, such a bight structure is ineffective for coupling various ossicular bones together, either because of the anatomy or because of the lack of the stability provided.
The present invention is directed to improvements in middle ear prosthetics.